Use Full Range of Motion
One problem with a sit-up is that, when you’re lying down, your hips and pelvis are fixed into position; do sit-ups often enough, and you create a pattern of dysfunction — you start using your hip flexors more than your abs, and you put unwanted stress on your spine.
A better solution that encourages more range of motion? The Hanging Leg Raise. Hang from a pull-up bar and slowly lift your knees toward your chest. (Going too fast will make you engage your hip flexors, and defeats the purpose). Don’t cut your range halfway, either. Round the spine — it’s ok to do here — and try to get the bottom of your sneakers to face the wall in front of you, with your knees touching your chest.Back to top